Which country first used a nuclear weapon in warfare?

• A. The United States of America
• B. The Union of Soviet Socialist Republics
• C. Japan
• D. China

Answer: (A)

The key idea is identifying who first deployed a nuclear weapon in combat. The United States carried out the first and only wartime use of a nuclear weapon, dropping atomic bombs on Hiroshima and Nagasaki in August 1945 during World War II. This establishes the United States as the earliest country to use nuclear weapons in warfare. The Soviet Union did develop and test a bomb in 1949 but did not use it in combat, Japan did not possess or deploy nuclear weapons during the war, and China did not have nuclear weapons until the 1960s.